In electronic devices used in computers, automobile parts, etc., heat dissipating elements such as heat sinks for dissipating heat generated from heat generating elements such as semiconductor devices, mechanical parts, etc., are used. For the purpose of enhancing the heat transfer efficiency to the heat dissipating elements, thermally conductive sheets are sometimes placed between heat generating elements and heat dissipating elements. For example, as such a thermally conductive sheet, Japanese Unexamined Patent Application Publication No. 2005-146057 (PTL 1) discloses a thermally conductive sheet in which carbon fibers are added as a heat transfer material and are oriented.
Such a thermally conductive sheet in which carbon fibers are oriented has a high heat conducting property in the thickness direction; however, since the carbon fibers have an electrically conductive property, the thermally conductive sheet cannot be applied to usage that requires a high electrical insulating property. To address this issue, Japanese Unexamined Patent Application Publication No. 2001-315244 (PTL 2) discloses a thermally conductive sheet in which an electrically insulating layer formed of an electrical insulating layer-forming composition is formed on one surface of a thermally conductive sheet in which carbon fibers are added as a heat transfer material and oriented.